1. Field of the Invention
The present invention relates to a device for measuring Echo Return Loss in a communication system. More specifically, the present invention is directed towards a device which accurately measures the Echo Return Loss produced by a two-two wire connection in a communication system.
2. Description of the Prior Art
Two-two wire connector circuits are commonly used in two-way communication systems, such as a telephone system. Two-wire telephone systems rely on a pair of wires to transmit and receive signals. However, as the distance between points in the communication system increase, the signal strength drops due to propagation losses.
In order to overcome the above difficulty, an amplifier can be placed within the signal path to boost the signal. However, since an amplifier can only boost a signal in one direction of a two-way communication system, two amplifiers are required (i.e., one amplifier to boost transmitted signals and another to boost received signals). Thus, the original two wires are split into four wires; two wires for transmitting signals and two wires for receiving signals. Following amplification, the four wires are recombined into two wires.
A simplified block diagram representing a two-two wire connector is shown in FIG. 1. On the left side of FIG. 1, two wire lines 10 and 20 connect to Point A; the signals are typically in the established voice frequency range. A transmission signal on wires 10 and 20 from Point A is split by network N1 into two transmission lines 12 and 14 to form a transmission path with respect to Point A. Along the path, the signal is boosted by at least one amplifier 16. After being amplified, the propagated signal is recombined by network N2 into wires 18 and 22, and continues on to Point B (e.g., a central office, another node, a user, etc.).
Similarly, transmission signals from Point B on wires 18 and 22 are split by network N2 into two transmission lines 24 and 26; lines 24 and 26 form a path with respect to Point A. Along the path, the signal is boosted by at least one amplifier 28. After being boosted, the signal is recombined by network N1 and sent along to Point A as a received signal.
The networks N1 and N2 rely primarily upon a series of transformers to split the signals. However, the transformers are not typically in perfect balance. They thus partially reflect a transmission signal back toward its origination point, otherwise known as an "echo". For example in FIG. 1, a portion of a signal sent from Point A to Point B is reflected by network N2 and returns to Point A. A user will thus hear the echo of his own voice.
The production of echoes due to imperfect balance in networks N1 and N2 can be minimized by adjusting the parameters which balance the network, e.g., a technician can fine tune network N2 by manipulating parameters A-C until the echo reduces to a desirable level. To this end, it is necessary to monitor the echo return loss of the two-two wire converter during manipulation of the network to identify those parameters which minimize the presence of echoes.
Although Echo Return Loss measurement devices are commercially available, their use of sophisticated circuitry makes them expensive, difficult to transport due to their bulk, and require manual interaction during measurement. In addition, these devices experience wide bandwidth noise which reduces the accuracy of the echo measurement.